(1) Field of the Invention
The present invention relates to a data recording and reproducing apparatus which encodes image and audio signals to record and reproduce these signals to and from a recording medium.
(2) Description of the Related Art
As a large-capacity optical-disc recording medium in which video and audio signals of a digital broadcast are recorded, BD (Blu-ray Disc) and HD (High-Definition) DVD are expected to be widely used. BD and HD DVD media are used for recording and reproduction with a laser beam having a shorter wavelength (405 nm) than that of DVD.
The standards for recording video and audio signals in a BD medium have already been established. As an application format used for rewritable media, standards which are called a BDAV (BD Audio/Visual) format have been established. This BDAV format adopts a stream format that complies with the digital broadcast standards. In addition, the BDAV format has good edit functions. The BDAV format, therefore, is characterized by specifications that are suitable for recording of broadcasted programs. According to the BDAV format, a received digital broadcast based on a certain compression method (encoding method) is recorded to a BD medium just as it is without changing the compression method. To be more specific, a video signal is received by the MPEG2 method; and an audio signal is received by the AAC (Advanced Audio Coding) method. Then, the video and audio signals are recorded to the BD medium just as they are.
On the other hand, as an application format that uses a BD medium, and that is used for read-only media, standards which are called the BDMV (BD MoVie) format have been established. Using this BDMV format, it is possible to realize a full interactive menu, and the like. Moreover, the BDMV format supports, for example, a picture-in-picture function, and a high compression stream such as the H.264 standards. Therefore, in comparison with the conventional DVD-Video, the BDMV format has specifications with high functionality. To be more specific, according to the BDMV method, a video signal is compressed by the H.264 method, whereas an audio signal is compressed by the AC3 (Audio Code number 3) method, before the video and audio signals are recorded.
Therefore, if a plurality of compression encoding methods are adopted for the same BD medium, it is necessary to change between these compression methods. When a compression method is changed (transcoded), it is required to change the compression method at higher speed and efficiently. For example, Japanese Patent Application Laid-Open No. 2001-110125 proposes the technology for changing a compression method without increasing product costs, and with material data (video/audio data) being transferred at a speed high than the normal speed. Here, compressed material data which is inputted at a transfer rate exceeding the normal speed is recorded in a medium just as it is. After that, using the unused time during which no access is made to the medium, the compressed material data is read out from the medium to transcode the material data in question, at the normal speed, to data based on a different compression method, and then the transcoded data is recorded in the medium again.